Conventionally, a vapor-compression type refrigeration cycle device is known to include, as components, at least: a compressor for compressing and discharging a refrigerant; a radiator for performing heat exchange between the discharged refrigerant from the compressor and an outside air; a decompression device for decompressing the refrigerant flowing from the radiator; and an evaporator for evaporating the decompressed refrigerant from the decompression device by causing heat exchange between the refrigerant and a blowing air that is to be sent into an air-conditioning space.
In such a refrigeration cycle device, it is desirable for a refrigerant flow amount flowing out of the decompression device to have a constant value regardless of the state of the refrigerant flowing into the decompression device, when a pressure difference between two pressures of the refrigerant on an inlet side and on an outlet side of the decompression device is constant. This is because, if the refrigerant flow amount flowing out of the decompression device changes, such change of the flow amount causes a change in a refrigerant circulation amount in the refrigerant cycle, thereby resulting in a change of cooling capacity of the evaporator for cooling the blowing air.
However, when, for example, a temperature change is caused for the outside air that exchanges heat with the refrigerant at the radiator, the state of the refrigerant may be changed from a gas-liquid two-phase state to a liquid state, or from the liquid-phase to the gas-liquid two-phase state, which is a change across a saturated-gas line. Such state change of the refrigerant across the saturated-gas line causes a drastic change of a refrigerant density, thereby leading to a drastic change of the refrigerant flow amount flowing out of the decompression device in some cases.
In view of such change, a radiator (i.e., a so-called sub-cool type condenser) or similar device is well-known, which cools the refrigerant to a supercooled liquid-phase state before discharging the refrigerant toward the decompression device, for the stability of the refrigerant flow amount flowing out of the decompression device. Further, because such a sub-cool type condenser cools the refrigerant to a supercooled liquid-phase state, enthalpy of the refrigerant at a refrigerant inlet side of the evaporator is decreased, and thereby refrigeration capacity of the evaporator is increased.
Further, the patent documents 1 and 2 disclose a configuration in which gas-phase and liquid-phase refrigerant flows into a nozzle of an ejector, which serves as a decompression device. Further, in the patent document 1, the refrigerant in the gas-liquid two-phase state causes to flow into the nozzle of the ejector so as to facilitate the boiling of the refrigerant at the nozzle, so that a nozzle efficiency is improved. In this case, the nozzle efficiency is defined as an efficiency of energy conversion that converts a pressure energy at the nozzle to a kinetic energy.
However, even when the above-described sub-cool type condenser is used as a radiator, the refrigerant flowing into the decompression device may have the gas-liquid two-phase state if the cooling of the refrigerant is insufficient due to, for example, a relatively high outside temperature or the like. In other words, the stabilization of the refrigerant flow amount flowing out of the decompression device may sometimes be difficult.
In contrast, when the refrigeration cycle device is configured such that, as shown in the patent documents 1 and 2, both of the liquid-phase refrigerant and the gas-phase refrigerant flow into the nozzle, the stabilization of the refrigerant flow amount flowing out of the decompression device is always expected, since, in such refrigeration cycle device, the state of the refrigerant flowing to the decompression device is securely controlled to be in the gas-liquid two-phase state regardless of the outside temperature.
However, the structure of the refrigeration cycle device in the patent documents 1 and 2 is complicated as a whole due to a trade-off of the above configuration that necessitates dedicated refrigerant passages for allowing both of the liquid-phase refrigerant and the gas-phase refrigerant to flow into the nozzle.